You know what'd be a good fix for this?

Be patient.

I don't like them either, but the timer is like 3 minutes long. If you really feel strongly about it, find who waits until the last second to roll, write their name down, and say mean things about them to yourself. Because that's really all you can do if politely asking everyone to roll won't work. And it's not really causing major issues other than wasting a few minutes of your time.